A received CDMA signal, rl(t), at lth (l≦L) receiver antenna element out of an L element array is denoted as per Equation 1:
                                                                                          r                  l                                ⁡                                  (                  t                  )                                            =                            ⁢                                                                    ∑                                          k                      =                      1                                        K                                    ⁢                                                            ∑                                              n                        =                                                  -                          ∞                                                                    ∞                                        ⁢                                                                  ∑                                                  m                          =                          1                                                M                                            ⁢                                                                        A                          k                                                ⁢                                                  s                                                      k                            ,                            n                                                                          ⁢                                                                              p                            k                                                    ⁡                                                      (                                                          t                              -                              nT                              -                                                              τ                                                                  k                                  ,                                  m                                                                                                                      )                                                                          ⁢                                                                              h                                                          k                              ,                              m                              ,                              l                                                                                ⁡                                                      (                            t                            )                                                                                                                                              +                                                                                                      ⁢                              n                ⁡                                  (                  t                  )                                                                                        Equation        ⁢                                  ⁢        1            where Ak is the signal amplitude of kth user, sk,n is the nth symbol of kth user, pk(t) is the signature waveform, including the spread code and pulse shaping waveform, of kth user. hk,m,l(t) is the channel response of mth path from lth antenna of kth user. n(t) is the combined interference which is typically due to the interference from other cells and additive channel noise. As is typical, this interference has the statistics of white Gaussian noise. The nth symbol of the kth user is of interest and the user index k and the symbol index n are dropped. After despreading the received signal for the kth user and nth symbol and for all M paths and all L antennas, Equation 2 is derived as follows:dm,l=Ahm,ls+zm,l  Equation 2where zm,l is the residual signal at the despreader for mth path and lth receiver antenna.
It is traditionally and commonly assumed that all zm,l (1≦m≦M,1≦l≦L) are Gaussian variables, and they are mutually uncorrelated across different multipath components and across different antennas. This assumption leads to a very simple and traditional receiver called a “Rake receiver” as shown in FIG. 1, where each Rake, or each branch in FIG. 1, estimates the complex channel weight gain (CWG) independently. As shown in FIG. 1, the antenna array has L elements, 1101 to 110L. For each element 110, a group of delays 11211 to 112LN, produce a group of delayed versions of the vector received by that element 110. Each delayed version is despread by a respective despreader 11511 to 115LN. Each despread output is input into a respective CWG generation circuit 10511 to 105LN. The derived CWGs are respectively applied to each despread output via respective multipliers 12011 to 120LN. The weighted outputs are combined by a combiner 125. The combiner 125 usually uses the maximum-ratio combining (MRC) in order to achieve the maximum signal-to-noise ratio at the combiner output. Mathematically, each Rake receiver estimates the channel gain gm,l, where gm,l is an estimate of Ahm,l, and noise variance σm,l2, where σm,l2, is an estimate of the power of zm,l) If MRC is used, the combiner generates
      ∑                  1        ≤        m        ≤        M                    1        ≤        l        ≤        L              ⁢                              d                      m            ,            l                          ⁢                  g                      m            ,            l                    *                            σ                  m          ,          l                2              .  Since gm,l is an estimate of Ahm,l and σm,l2 is an estimate of the power of zm,l, the generation of gm,l for any one particular Rake receiver is independent of all other Rake receivers. This approach assumes that all zm,l (1≦m≦M,1≦l≦L) are zero mean Guassian variables, which are mutually uncorrelated across different multipath components and accross different antennas. However, there is correlation across the multipath components and antennas, which result in inter symbol interference (ISI). Also, due to correlation between multiple user also over the multipath components and antennas, multiple access interference (MAI) is also increased. Accordingly, the receiver performance is degraded.
Accordingly, it is desirable to have alternate receiver configurations.